Downhole tool shock absorber

ABSTRACT

Shock absorbers for downhole tools. The shock absorbers entailing a columnar body having a wall including a plurality of cells, and a retainer adapted to retain the shock absorber on the tool body. The retainer also adapted to transfer an impact force to the shock absorber.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to shock absorbers. More particularly, the invention relates to shock absorbers for use with downhole apparatus.

2. Background Art

In the oil and gas field, downhole apparatus or tools are used to perform various subsurface operations, generally in a wellbore. Downhole tools comprise any one of various apparatus used in subsurface measurements, exploration, production, and monitoring operations as known in the industry. Typical downhole tools are configured with elongated or tubular-type bodies to facilitate their deployment and transport through subsurface formations. In applications where there are multiple tool bodies, the tool bodies are joined together to form a tool string (e.g., a multi-measurement tool string). A typical downhole operation involves lowering the downhole tool(s) into the wellbore on the end of a drill pipe or wireline or coiled tubing. As the downhole tool is lowered into the wellbore, the bottom of the tool may strike a ledge on the wall of the wellbore or the bottom of the wellbore. The tool body at the bottom of the downhole tool absorbs impact loads when the tool bottom strikes the wall or wellbore bottom. In cases where the bottom of the tool body contains an instrument, it is desirable to provide a shock absorbing mechanism at the tool bottom to protect the instruments from shock and impact loads.

Myriad types of shock absorbers are used in industry for a multitude of applications. U.S. Pat. No. 6,472,043 describes a shock absorber for use in aerospace applications and automotive crash testing. The shock absorber entails a honeycomb block with a plurality of cylindrical cells arranged in parallel. A need remains for improved shock absorption mechanisms for subsurface applications.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a shock absorber for a downhole tool. The shock absorber including a columnar body having a wall comprising a plurality of cells. In one embodiment, the columnar body includes a hollow core. The columnar body may be formed of a metal, an alloy, or a composite. The shock absorber includes means of retaining the columnar body on a downhole tool. The means of retaining the columnar body is preferably configured to transfer impact loads to the columnar body.

In another aspect, the invention relates to a downhole tool. The downhole tool including a tool body, a shock absorber having a columnar body, the columnar body having a wall comprising a plurality of cells, and a retainer adapted to retain the columnar body on the tool body.

In another aspect, the invention relates to a method of mounting a shock absorber on a downhole tool. The method comprising disposing the shock absorber at one end of the body of the downhole tool, the shock absorber having a columnar body with a wall including a plurality of cells; and retaining the columnar body on the tool body.

Other features and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic of a shock absorber according to an embodiment of the invention.

FIG. 1B is an enlargement of the honeycomb cell structure shown in FIG. 1A.

FIG. 1C shows the honeycomb cell structure of FIG. 1B filled with sealant material.

FIG. 1D illustrates a technique of forming a shock absorber according to an embodiment of the invention.

FIG. 2 is a force versus displacement curve for a shock absorber in accord with the invention.

FIG. 3 shows a retainer for a shock absorber according to an embodiment of the invention.

FIG. 4 shows a downhole tool incorporating a shock absorber according to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1A illustrates a shock absorber 100 according to one embodiment of the invention. The shock absorber 100 can be mounted on a downhole tool and used to absorb shock and impact loads that would otherwise be absorbed by the downhole tool or tool components. The shock absorber 100 includes a columnar body 102 having end faces 104, 106. The columnar body 102 can be formed solid or with a hollow core. If a solid columnar body 102 is used, the crush load of the body should be determined to ensure that the necessary protection is provided to the tool. The shock absorber 100, not the tool, should deform in response to impact loads. In a preferred embodiment, the columnar body 102 is hollow, i.e., has cavity 105.

In one embodiment, a wall 108 of the columnar body 102 has a honeycomb structure 108 a. As shown in FIG. 1B, the honeycomb structure 108 a is composed of cells 110 defined by webs 112. The webs 112 extend longitudinally between the end faces (104, 106 in FIG. 1A) of the columnar body (102 in FIG. 1A). The thickness of the webs 112 may be constant or vary between the end faces 104, 106. In the illustration, the cross-sectional shape of the cells 110 is hexagon. However, the invention is not limited to this shape. For example, the cross-sectional shape of the cells 110 could be a triangle, square, octagon, or other appropriate shapes.

Returning to FIG. 1A, the magnitude of the impact loads that can be absorbed by the shock absorber 100 depends on the geometry of the cells (110 in FIG. 1B), the cell density of the honeycomb structure 108 a, the thickness of the webs (112 in FIG. 1B), the thickness of the wall 108, and the properties of the material used in making the columnar body 102. The columnar body 102 is made of a material capable of absorbing impact energy and maintaining its chemical integrity in a subsurface environment. The material could be a metal or an alloy or a composite. Preferably, the material has a high strength-to-weight ratio. One example of a material suitable for use in making the columnar body 102 is an aluminum alloy. The aluminum alloy may be anodized to increase its ability to withstand subsurface exposure.

FIG. 1C shows the cells 110 of the honeycomb structure 108 a filled with a sealant material 114 according to another embodiment of the invention. The sealant material 114 could be any suitable material, such as a curable material (e.g., epoxy). The sealant material 114 should be able to maintain its chemical integrity in a subsurface environment. Filling the cells 110 with the sealant material 114 can enhance the mechanical properties of the columnar body (102 in FIG. 1A) while minimizing the surface area exposed to attack from external fluids and chemicals.

Embodiments of the columnar body 102 can be formed by laminating corrugated sheets of material (116 in FIG. 1D) and shaping the laminate into a columnar body. After shaping the laminate, a sealant material, such as epoxy, could be pumped into the voids (118 in FIG. 1D) formed by the laminated corrugated sheets to form the structure shown in FIG. 1C. Depending on the sealant material(s) used, the material can be applied at room temperatures as known in the art. If the sealant material is too viscous, a viscosity-reducing (or thinning) agent may be added to the sealant as needed and the structure can be heat treated to cure the sealant material. The temperature, pressure, and duration of the curing process depend on the sealant material. The use of a sealant material forms an additional bond between the corrugated sheets, making the columnar body 102 more robust as desired.

The invention is not limited to forming the columnar body 102 by laminating corrugated sheets of material and shaping the laminate. The columnar body 102 could also be formed by extrusion. The webs 112 could be solid or may have a foamed (porous) structure. The foamed webs could be made by known metal foaming processes. One such process involves compacting a mixture of metal powder and foaming agent and heat-treating the compacted body near the melting point of the metal. The metal expands and develops pores during the heat treatment. Other techniques may be used to form the columnar bodies to implement the invention as known in the art.

FIG. 2 shows a force vs. displacement curve for a shock absorber having a columnar body with a honeycomb structure. This honeycomb structure is made from corrugated sheets of aluminum alloy, available from Hexcel Corporation, Stamford, Conn. The columnar body has an outer diameter of 2.25 in (5.72 cm) and an inner diameter of 1.7 in (4.32 cm). The crush strength of the columnar body is 1350±203 psi (9,310±1400 kPa). The lower limit of the crush strength 1,147 psi (7,910 kPa) amounts to a crush force of approximately 2,000 lbf (8,896 N). This means that the shock absorber would elastically absorb loads smaller than 2,000 lbf (8,896 N) and plastically deform at 2,000 lbf (8,896 N) or higher. When the columnar body (102 in FIG. 1A) is made of a metal or alloy, the columnar body could be pre-crushed (based on the desired load to plastically deform the absorber) to eliminate peak load.

A retainer is used to retain the shock absorbers 100 of the invention on the downhole tools. Those skilled in the art will appreciate that there are a variety of ways one can mount and retain the shock absorbers of the invention on a downhole tool. A desirable feature of the retainer is that it should accommodate crushing of the shock absorber due to absorption of impact loads. For example, the retainer can include telescoping parts that allow the length of the retainer to change as the shock absorber is crushed. Another desirable feature in a retainer is for it to transfer impact loads to the shock absorber.

FIG. 3 shows a retainer 300 for the shock absorber 100 according to one embodiment of the invention. The retainer 300 includes a lower body 302 and an upper body 304. The lower body 302 includes a base 306 and a hub 308 extending from the base 306. The shock absorber 100 is mounted on the base 306 and about the hub 308. Lateral motion of the shock absorber 100 is limited by the hub 308. Retention slot 310 and alignment slot 312 are provided inside the hub 308. The upper body 304 includes a tab 314 that can be inserted in the alignment slot 312 and the retention slot 310. When the tab 314 is in the alignment slot 312, the lower body 302 can be slipped onto or separated from the upper body 304. For clarity of illustration, FIG. 3 does not show a key slot or groove in the lower body 302 configured to guide the tab 314 into position within the retention slot 310. Some embodiments can be configured with multiple slots 310, 312 and/or tabs 314.

When the tab 314 is in the retention slot 310, the upper body 304 is coupled to the lower body 302. The tab 314 can move within the retention slot 310, allowing movement of the lower body 302 relative to the upper body 304 when the shock absorber 100 is crushed. The lower body 302 transfers impact loads to the shock absorber 100. Vertical motion of the shock absorber 100 is limited by a shoulder 316 on the upper body 304. An embodiment can also be implemented with spring means disposed between the upper body 304 and lower body 302, abutting against the shoulder 316 on the upper body and the top of the lower body (not shown). The spring means would absorb some of the impact load and aid in maintaining the body 302 from twisting or uncoupling from the upper body 304. In one embodiment, the upper body 304 also includes threads 318 for engaging the downhole tool. Other configurations for engaging the upper body 304 to a downhole tool may also be (e.g., snap-fit mechanisms, fasteners, clamps, welding) used to implement the invention as known in the art. Alternatively, the downhole tool can also be pre-formed with its end adapted to accept the lower body 302 and shock absorber 100 (not shown).

FIG. 4 shows a downhole tool 400 having tool bodies 402 joined together to form a tool string. The tool bodies 402 are configured to perform a downhole operation, such as formation testing. A shock absorber 100 of the invention is disposed at the bottom of the downhole tool 400 using, for example, the retainer 300 (shown in FIG. 3). The downhole tool 400 with the shock absorber 100 is lowered into a wellbore 404 using, for example, a wireline 406 or other suitable conveyance mechanism as known in the art. As the downhole tool 400 is lowered, the retainer 300 may strike a ledge on the wall of the wellbore 404 or the bottom of the wellbore 404. Impact loads applied to the retainer 300 are transferred to the shock absorber 100 retained in the retainer 300. The shock absorber 100 absorbs the impact loads, thereby protecting instruments in the downhole tool 400 from damage.

A process for mounting a shock absorber 100 on a downhole tool 400 according to the invention entails disposing the shock absorber at one end of the downhole tool body (shown in FIG. 4), the shock absorber having a columnar body 102 with a wall including a plurality of cells as described herein. The columnar body is then retained on the tool body as described herein. The shock absorbers 100 of the invention are not limited to external use. The shock absorbers 100 can also be implemented on tools configured for transport through other tools or conduits. One such application entails the disposal of a shock-absorber-equipped run-in tool in a drill collar, at the earth surface, for transport through the collar to a desired subsurface location within the drill string (See e.g., U.S. Pat. No. 6,577,244).

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention. For example, shock absorber embodiments of the invention may also be formed in quadrants or sectors of a cylindrical surface of revolution which, when juxtaposed together, would comprise or constitute a columnar body (not shown). It will also be appreciated that the present invention is applicable to, and can be implemented in, any field where shock absorption is desired; it is not limited to downhole tools or subsurface applications. 

1. A shock absorber for a downhole tool, comprising: a columnar body having a wall comprising a plurality of cells.
 2. The shock absorber of claim 1, wherein the columnar body comprises a hollow core.
 3. The shock absorber of claim 2, wherein the columnar body is formed of a material selected from a group consisting of a metal, an alloy, and a composite.
 4. The shock absorber of claim 2, wherein the columnar body is made of an aluminum alloy.
 5. The shock absorber of claim 1, wherein the columnar body is pre-crushed.
 6. The shock absorber of claim 1, wherein the cells contain a sealant material.
 7. The shock absorber of claim 1, further comprising means for retaining the columnar body on a downhole tool.
 8. The shock absorber of claim 7, wherein the means for retaining the columnar body is adapted to transfer impact loads to the columnar body.
 9. The shock absorber of claim 7, wherein the means for retaining the columnar body comprises telescoping parts adapted to accommodate deformation of the columnar body due to impact loads.
 10. The shock absorber of claim 1, wherein the wall is made from a laminate of corrugated sheets of material.
 11. The shock absorber of claim 10, wherein the material comprises an aluminum alloy.
 12. A downhole tool, comprising: a tool body; a shock absorber having a columnar body, the columnar body having a wall comprising a plurality of cells; and a retainer adapted to retain the columnar body on the tool body.
 13. The downhole tool of claim 12, wherein the columnar body comprises a hollow core.
 14. The downhole tool of claim 12, wherein the columnar body is formed of a material selected from a group consisting of a metal, an alloy, and a composite.
 15. The downhole tool of claim 12, wherein the columnar body is made of an aluminum alloy.
 16. The downhole tool of claim 12, wherein the cells contain a sealant material.
 17. The downhole tool of claim 12, wherein the wall is made from a laminate of corrugated sheets of material.
 18. The downhole tool of claim 12, wherein the retainer comprises telescoping parts adapted to accommodate deformation of the columnar body due to impact loads.
 19. The downhole tool of claim 12, wherein the shock absorber is disposed on an end of said tool body.
 20. The downhole tool of claim 19, wherein the retainer is adapted to transfer impact loads to the columnar body of said shock absorber.
 21. A method of mounting a shock absorber on a downhole tool, comprising: disposing said shock absorber at one end of the body of said downhole tool, said shock absorber having a columnar body with a wall including a plurality of cells; and retaining said columnar body on the tool body.
 22. The method of claim 21, wherein the wall of said columnar body is made from a laminate of corrugated sheets of material.
 23. The method of claim 21, wherein retaining the columnar body comprises disposing a retainer on the tool body, said retainer adapted to accommodate deformation of the columnar body due to impact loads. 